Subassembly for use in manufacturing a tubular product

Abstract

A method of manufacturing an externally clad tubular product employing a tubular host such as steel, including the steps of plating the external surface of the tubular host with a low melting point bonding metal alloy, assembling a tubular clad member, such as of nickel base alloy, over the plated tubular host, circumferentially welding one end of the cladding member to one end of the host member and welding the other ends in such a manner as to incorporate a metallic gas reservoir, thus forming a subassembly. The annular space formed in the subassembly between the interior of the cladding member and the exterior of the tubular host is evacuated of water vapor and oxygen. The evacuated subassembly is heated to about 1650° to 2100° F. thereby melting the bonding metal alloy, and the heated subassembly hot rolled to metallically bond the cladding member to the tubular host by means of the mechanism of liquid interface diffusion bonding.

What is claimed is: 
     
       1. For use in the manufacture of an externally clad tubular product a subassembly comprising: a tubular metallic host having a first and second end, the external tubular surface being plated with a low melting point bonding metal alloy;   a tubular metallic cladding member having a first and second end, the cladding member being telescopically assembled over said tubular host and having the first end thereof circumferentially welded to the first end of said tubular host; and   a metallic tubular bag welded to said tubular host adjacent the second end thereof and to said cladding member adjacent said second end forming a closed space including the annular area between the interior of said tubular cladding member and the exterior of said tubular host member, the tubular bag having a small diameter opening therein, said closed space being sufficiently evacuated and filled with an inert gas so that the water and oxygen therein is substantially at a level below a dew point of about -60° F.   
     
     
       2. A subassembly according to claim 1 wherein said low melting point bonding metal alloy is selected from a group comprising nickel phosphorus, nickel boron, nickel chromium phosphorus, chromium phosphorus and mixtures thereof. 
     
     
       3. A subassembly according to claim 2 wherein said low melting point bonding metal alloy is nickel phosphorus composed of about 88 to 98 percent by weight nickel and about 2 to 12 percent by weight phosphorus. 
     
     
       4. A subassembly according to claim 3 wherein said low melting point bonding metal alloy is a compound comprising about 88 to 98 percent by weight nickel, about 2 12 percent by weight phosphorus and about 0.5 to 1 percent by weight boron. 
     
     
       5. A subassembly according to claim 1 wherein the exterior surface of said tubular host member is coated with flux material. 
     
     
       6. A subassembly according to claim 5 wherein said flux material is composed essentially of cryolite.